I believe the G-Body Swap is fairly common.
Maximum Torque Specialties out of Devan, Wisconsin, sells a lot of performance parts for the 472/500 Motors. They sell some universal motor mount kits. They may sell headers that are ready to go for the G-Body swap. There are at least a couple of other places selling parts out there, but I have dealt with MTS and the customer service is good, you deal with the owner directly.
You will need a rear sump oil pan from a Eldorado. The Devilles used a center sump oil pan which won't clear your cross member.
The 472/500 require a transmisson with the Buick, Olds, Pontiac Bolt Pattern.
I would recommend that unless you are running a overdrive trans that you stay will a rear end ratio in the 3:00 - 3:30 range. These motors don't rev very high. I have a 3:73 in my 472 Camaro and its too much on the highway.
I have had my 472 '70 Camaro for 15 years. I have a 70 472 with 10.5:1 Compression, ported factory heads, factor Single Plane Manifold, Holley 800, factory manifolds, and an MTS Mid Grind Cam.
If you can get headers and an aftermarket intake it should really open it up.
81 Monte Carlo - LS1 6-spd (conversion in process)
70 Camaro 472 Cadillac Power
07 Silverado Z71 Crew Cab